Tests of the effects of acute and chronic administration of caffeine on autonomic nervous system (ANS) functioning have been carried out to evaluate the role of ANS activity in behavioral and subjective effects of this drug. A test of attention using a reaction time method is included. The test protocol involves recording peripheral indicators of ANS activity such as skin conductance (SC), heart rate (HR), and skin temperature during a session consisting of a rest period, presentation of a series of simple tones to which no response is required, and the reaction time task. Studies have been carried out on the effects of the acute administration of two doses of caffeine and a placebo in 6-13 year old boys and in men, and a pilot study and major study of chronic (2 week) caffeine intake in children. The effects of both acute and chronic administration of caffeine were increases in SC indices of arousal but some trends toward decreases in HR. The SC results are consistent with the hypothesis that caffeine can be considered a pharmacologic model for anxiety, but the HR effects suggest the model is imperfect. In a current study, an acute dose protocol with caffeine will be done on children with anxiety disorders and on offspring of adults with anxiety disorders. This will test the hypothesis, for which there is evidence in adults, that patients with anxiety disorders are more sensitive to caffeine than controls. In addition, the study tests the hypothesis that the hypersensitivity is under genetic influence.